As we were outbound on our latest trip (previous entry), we stopped at a dump station to make sure we were completely empty for the 3 nights of dry camping. On our trailer we have a black tank flush device. It is a connector for a hose that is behind a little door by our dump valves. It allows you to hook a hose from the dump station or your own water tank. When you apply water to it, it squirts inside the black tank to help ‘dislodge’ anything that may be stuck inside there.
I hooked it up to the shore water at the dump station and turned it on. Water started gushing out our holding tank belly pan. It was more interesting since my valve repair added many new rivets and the water came out of this rivets in a most interesting pattern. So I will be going back under the trailer, removing the rivets and the cover plate. Hopefully the hose just became disconnected and all I have to do is reconnect it.